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Difficulty: MediumBreast and Endocrine Surgery

A 55-year-old woman presents to the surgical clinic for evaluation of a neck mass that she noticed two weeks ago while swallowing. She reports a 6-month history of profound fatigue, cold intolerance, dry skin, and a 4.5-kg (10-lb) weight gain. Her past medical history is significant for a severe postpartum hemorrhage requiring multiple blood transfusions 20 years ago. She takes no daily medications. Her temperature is 36.5°C (97.7°F), blood pressure is 110/70 mmHg, and pulse is 58/min. Physical examination reveals a 2.5-cm, firm, non-tender, mobile nodule in the right lobe of the thyroid gland. There is no cervical lymphadenopathy.

Laboratory studies show:
TestResultNormal Range
Thyroid-stimulating hormone (TSH)0.1 mIU/L0.4–4.0 mIU/L
Free T40.5 ng/dL0.9–1.7 ng/dL

Ultrasound of the neck demonstrates a 2.5-cm solid, markedly hypoechoic nodule with irregular margins in the right thyroid lobe. Which of the following is the most appropriate next step in the management of this patient's thyroid nodule?

  1. A
    Radionuclide thyroid scintigraphy
  2. B
    Initiation of methimazole therapy
  3. C
    Observation with repeat ultrasound in 6 months
  4. Fine-needle aspiration biopsy of the thyroid noduleAnswer
  5. E
    Prescription of propranolol

Answer

Fine-needle aspiration biopsy of the thyroid nodule
The standard diagnostic workup for a newly discovered thyroid nodule begins with a serum TSH. Typically, a low TSH prompts a radionuclide thyroid scan to identify a 'hot' nodule. However, this patient's labs (low TSH and low free T4) and clinical history (postpartum hemorrhage, fatigue, weight gain) are diagnostic of central (secondary) hypothyroidism, likely Sheehan syndrome. Because her thyroid gland is not autonomously hyperfunctioning, a radionuclide scan will not provide useful information regarding a 'hot' nodule. Therefore, the nodule must be evaluated strictly based on ultrasound features. The patient's nodule is 2.5 cm, solid, markedly hypoechoic, and has irregular margins—all highly suspicious features for thyroid malignancy. The appropriate next step is a fine-needle aspiration biopsy to evaluate for thyroid cancer.

Step-by-Step Solution

1
Interpret the laboratory findings.
The patient has both a low TSH (0.1 mIU/L) and a low free T4 (0.5 ng/dL).
This laboratory pattern indicates central (secondary) hypothyroidism, rather than primary hyperthyroidism, which is further supported by her history of postpartum hemorrhage (Sheehan syndrome) and hypothyroid symptoms.
2
Determine the appropriate algorithm for the thyroid nodule.
The nodule must be evaluated using standard ultrasound criteria, bypassing the radionuclide scan.
Although the TSH is low, the thyroid gland is not autonomously functioning. Therefore, a radionuclide scan is not indicated, as the low TSH is driven by pituitary failure, not an autonomous 'hot' nodule.
3
Evaluate the ultrasound features to determine the final next step.
The nodule is 2.5 cm, solid, markedly hypoechoic, and has irregular margins.
These are highly suspicious sonographic features for malignancy, making a fine-needle aspiration (FNA) biopsy explicitly indicated to establish a tissue diagnosis.

Key Concept

In patients with a thyroid nodule and central hypothyroidism (low TSH, low Free T4), the low TSH does not indicate an autonomously functioning thyroid gland. Therefore, a radionuclide scan is bypassed, and the nodule is evaluated with fine-needle aspiration biopsy based on sonographic criteria.
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Topics

Breast and Endocrine Surgery

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